过冷核态池沸腾中的Marangoni效应

分析了过冷核态池沸腾过程中气泡横向运动现象,指出其成因在于相邻气泡界面温度差引起的Mara- ngoni对流对周围液体的吸引.通过对该流动的尺度分析,得到了气泡横向运动特征速度及其可观测度的估算公式,其预测结果与实验观测相一致.特别是对极细小的初始核化气泡,该公式预测了强烈的横向Marangoni对流会导致气泡顶端微射流的形成.该效应在加热面水平向下或微重力沸腾等气泡脱落频率较低的情形中尤为重要.

Marangoni Effect in Subcooled Nucleate Pool Boiling

The lateral motion of bubbles attached to the heater surface during nucleate pool boiling of subcooled liquids is studied in the present paper. It is assumed that there exists the Marangoni convection surrounding a discrete vapor bubble due to the temperature difference acting on the interface between vapor and liquid. The mutual entrainment of adjacent bubbles in the Marangoni convection might drive bubbles toward each other during nucleate boiling of a subcooled liquid. This kind of motion promotes coalescence of adjacent bubbles. A scaling analysis on such flow is presented. The characteristic velocity of the lateral motion is obtained approximately. Furthermore, an approximate equation for estimating the observability of such motion is also presented. The predictions are consistent with the experimental observations. Moreover, it is predicted that the intensity of the Marangoni convection may be very high for fine bubbles initiated at some active cavities on the heater surface, which will result in the micro-jet at the top of the bubble. The effect would be especially important in cases where the bubble release rate is low such as boiling on horizontal down-facing surfaces and boiling in microgravity.